Abstract: Using finite element method,the authors analyzed the manufacture and installation process of cross-rail,fully taking into account measuring impact of the camber curve under the different ways,and compared the installation difference between the manufacture and the work condition.The measure result was explained and the deviation reason was found.The error of the camber curve came from the clamping difference between the manufacture and the work condition.The authors advice that the reverse curve of deformation according to the work condition cannot be used directly to manufacture,when the clamping condition is different from the work condition.A new camber curve was provided,and the error,brought by the clamping condition,was compensated,and the deviation of the camber curve was eliminated.